In this lesson, we'll discuss the materials needed to make soil--organic matter and parent material. We'll also talk about the two main processes that break down rocks: weathering and erosion.

Soil Formation

Salli needs soil for her garden and decides she will make her own. She realizes that she does not know how soil forms. She goes to a garden store to find out what she needs to make soil. The clerk explains that she needs rocks to grind, dead leaves, and a lot of time.

Soil is formed when two substances are mixed together over a long period of time. The two main ingredients in soil are organic matter and parent material. Let's explore these two components of soil below.

What's In Soil?

Organic Matter

Organic matter is made of decomposed plants and animals. Plant parts such as leaves, fruit, and limbs fall to the ground and break down into smaller pieces. These smaller pieces are called organic matter and add nutrients to the soil. Insects and animals that die also decompose and break down into the soil.

Soil is made of organic matter and parent material.

Parent Material

Parent material is another main ingredient in soil. Parent material is made of rocks that have broken down over a really long time. Rocks are broken down by two main processes called weathering and erosion, which we will explore below.

Processes in Soil Formation: Weathering and Erosion

Weathering is when the temperature in an environment changes and cause rocks to break apart. When it is too hot or too cold, rocks break and the small pieces become part of the soil. For example, when water freezes around a rock, the ice expands and pushes the rock apart when it melts. On the other hand, heat causes rocks to expand and break. These broken down rock parts become part of the soil.

Erosion also breaks down rocks. Erosion is when water or wind moves the earth's surface. Rivers are a good example of erosion because the water pushes soil down the river. Soil, plants, and rocks are washed from the banks and pulled down the river. Water and wind rub against rocks, which causes them to break down into sand or powder that becomes part of the soil.

Lesson Summary

Organic matter and parent material are the two main ingredients in soil. Weathering and erosion are the two main processes that break down rocks that become soil. Making soil takes a really long time because nature has to go through these time-consuming processes.

Summary:

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